The present invention relates to an oscillator and semiconductor integrated circuit device, and relates in particular to an oscillator within a semiconductor integrated circuit including an inductance element and capacitance element for compensating the temperature characteristics, and a semiconductor integrated circuit device containing an internal oscillator, and utilizing the output signal of that oscillator as a reference clock.
Semiconductor integrated circuits in the related art requiring a relatively accurate clock pulse typically used a piezoelectric oscillator such as crystal oscillator coupled to the external terminals of the semiconductor integrated circuit. An internal amplifier circuit within the semiconductor integrated circuit was made to oscillate, to generate the clock pulse required for semiconductor integrated circuit operation. However, to make the mounting substrate within the semiconductor integrated circuit smaller and at a lower cost, the LC oscillator is being made an internal component within the semiconductor integrated circuit. Forming the inductance element L and the capacitance element C over the semiconductor substrate in the semiconductor integrated circuit eliminates the need for externally attaching a crystal oscillator to an external portion of the semiconductor integrated circuit so that the intrinsic value of the semiconductor integrated circuit is enhanced and the mounted substrate can be achieved at a low cost and a miniaturized shape. The ideal oscillation frequency of the LC oscillator is known to be 1/(2π√(LC)). When adjusting the oscillator circuit frequency becomes necessary, the frequency can be adjusted by correcting the error in the oscillation frequency by adjusting the L (inductance) or C (capacitance).
Making this type of LC oscillator an internal component within the semiconductor integrated circuit requires that the LC oscillator provide stable oscillation at the specified frequency in semiconductor integrated circuits having variations or irregularities in the manufacturing process, supply voltage, and operating temperature, etc.
Among the above irregularities, the effects of those irregularities stemming from the manufacturing process can be suppressed by methods such as measuring the process variations by screening and other techniques after chip selection. Moreover, irregularities stemming from the supply voltage can be compensated by forming a fixed voltage supply such as a band-gap reference within the semiconductor integrated circuit. Suppressing effects from irregularities stemming from the manufacturing process and irregularities stemming from the supply voltage is comparatively easy to accomplish. However, compensating for irregularities due to the operating temperature to achieve a specified (fixed) oscillation frequency is not easily accomplished. Examples of the related art as countermeasure solutions for operating temperature irregularities in these types of semiconductor integrated circuits having internal LC oscillators are disclosed in Japanese Unexamined Patent Publication No. 2010-50973 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-531404. The temperature compensation in these type of internal oscillators implemented by the method disclosed in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-531404 is complicated and tends to require a larger circuit scale.
The method in Japanese Unexamined Patent Publication No. 2010-50973 on the other hand discloses a comparatively simple method for compensating the temperature characteristics. FIG. 16 is a circuit diagram showing a (temperature compensated) LC oscillator tank operating at the temperature null phase as described in Japanese Unexamined Patent Publication No. 2010-50973. The LC oscillator tank in Japanese Unexamined Patent Publication No. 2010-50973 shown in FIG. 16 amplifies the resonance occurring in the inductance element L and capacitance element C using an amplifier circuit not shown in the drawing and causes oscillation. Generally making the wiring of inductance element L longer is unavoidable to achieve an inductance element L in the semiconductor integrated circuit so that the parasitic resistance rL value of the inductance element L becomes a somewhat large value. The parasitic resistance rL for the inductance element L can be considered an equivalent circuit where the inductor L and resistor rL are coupled in series as shown FIG. 16. In contrast to the resistance value of this parasitic resistance rL, the value of the parasitic resistance rC coupled in series with the capacitor C formed in the semiconductor integrated circuit is not as large as the rL (resistor) value. Moreover, using a parasitic resistance rC having a large value is traditionally considered a drawback in view of greater noise jitter.
In regards to this issue, the description in paragraph 0039 of Japanese Unexamined Patent Publication No. 2010-50973 discloses that a non-temperature dependent oscillation frequency can be achieved by coupling the resistor rC for attaining rC=rL, in series to the condenser C. The resistance rC in Japanese Unexamined Patent Publication No. 2010-50973 is in other words, not simply a parasitic resistance but a resistance rC attained by coupling a condenser in serial to a resistance rC achieving rC=rL, in order to obtain a non-temperature dependent oscillator
Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-531404 discloses a monolithic clock generator including a temperature compensator to correct the resonant frequency according to the temperature. FIG. 4 of Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-531404 discloses a resistor Rc (450) coupled in series to a capacitance element Cf (440). However, paragraph 0034 in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-531404 states that, “one must understand that though shown separately, the corresponding resistance (or impedance) RL445 and Rc450, are respectively unique to the inductor 435 and capacitor 440; and are one part of the manufacturing process; therefore these are not additions made to the inductor 435 and capacitor 440 and moreover are not components separate from this inductor and capacitor,” in the description. So the resistance Rc (450) is at most only a parasitic resistance, and different from the resistance rC in which rC=rL of Japanese Unexamined Patent Publication No. 2010-50973 and that is continually rendered as needed.